Since a .bmp picture is bigger than for example a .jpg picture,
will a game with only bmp-images have a bigger compiled file
than a game made only with .jpg pictures ?
Well, ags can't even import jpg pictures, can it?
But anyway, the format you import doesn't make a difference to the size, no. AGS stores the images internally in it's own way, room backgrounds are compressed using gif style compression, and sprites are not (which is one reason why zipping makes a difference)
The only things that make a difference are image size/resolution and colour depth, a 256 colour image will be a lot smaller than a 16 bit one.
Also, the number of colors and the complexity of the images matters, AFAIK, so makeing simpler bgs or sprites might drop the file size...
Scotch is spot on. Don't worry too much about the size of your Compiled folder - try zipping it up and you may be pleasantly surprised.
Yeah, zipping makes a huge difference, Just as an example, my latest game is 42MB in the compiled folder and when zipped compresses to 3.26MB, which is quite a significant difference.